Certain embodiments of the present invention relate to an ultrasound machine for displaying an image of moving structure. More particularly, certain embodiments relate to displaying a color characteristic representing the moving structure.
Echocardiography is a branch of the ultrasound field that is currently a mixture of subjective image assessment and extraction of key quantitative parameters, of cardiac wall function has been hampered by a lack of well-established parameters that may be used to increase the accuracy and objectivity in the assessment of, for example, coronary artery diseases. Stress echo is such an example. It has been shown that the subjective part of wall motion scoring in stress echo is highly dependent on operator training and experience. It has also been shown that inter-observer variability between echo-centers is unacceptably high due to the subjective nature of the wall motion assessment.
Much technical and clinical research has focused on the problem and has aimed at defining and validating quantitative parameters. Encouraging clinical validation studies have been reported, which indicate a set of new potential parameters that may be used to increase objectivity and accuracy in the diagnosis of, for instance, coronary artery diseases. Many of the new parameters have been difficult or impossible to assess directly by visual inspection of the ultrasound images generated in real-time. The quantification has typically required a post-processing step with tedious, manual analysis to extract the necessary parameters.
Much of the prior art describes techniques for color mapping of estimated imaging parameters such as tissue velocity and strain rate. A fixed mapping of a continuous range of color hues is typically used to indicate positive velocities or strain rates and a second fixed mapping of a continuous range of color hues is used to indicate negative velocities or strain rates. This type of color encoding makes it easy to identify reversals in velocities or strain rates. Timing information related to the velocity or strain rate reversals is also easy to extract from M-mode displays.
However, the tissue velocity imaging (TVI) and strain rate imaging (SRI) modes and associated color mapping schemes in the prior art are not, by themselves, well suited for visual determination of other parameters, such as xe2x80x9cpeakxe2x80x9d mean velocities or xe2x80x9cpeakxe2x80x9d mean strain rates over a portion of the cardiac cycle. Herein, xe2x80x9cpeakxe2x80x9d refers to the largest mean parameter value within a set of mean parameter values. Typically, a Nyquist velocity and associated pulse repetition frequency is set in order to avoid aliasing. Most of the actual mean velocities are only a small fraction of the peak mean velocity that, in cardiac imaging from apex, typically may be measured at the mitral ring during the E-wave in diastole. As a result, most regions in the image are colored with only small variations of the color hue selected for lower positive and/or lower negative mean velocities. Quantitative assessment of parameters such as peak mean velocities or peak mean strain rates from 2-D images has been difficult, even in lucky situations, with a good spread of measured imaging parameters. It has, therefore, been necessary to resort to post-processing techniques and manual extraction of the digital information for estimation of quantitative peak values.
Academic work has been done for validation of peak mean systolic velocities as an indicator of, for example, ischemia in stress echo. Clinical results indicate that a reduction in peak mean systolic velocities at peak exercise is a good predictor of coronary artery diseases. Therefore, it is useful to design a display mechanization that makes it easy to visually assess above average and/or peak mean systolic velocities in a quantitative manner.
U.S. Pat. No. 5,820,561 (Olstad, et al, issued Oct. 13, 1998) describes extracting timing information from estimated parameters (such as velocity of curved organs) during a cardiac cycle and color encoding the timing information for display.
U.S. Pat. No. 5,910,119 (Lin, issued Jun. 8, 1999) describes a technique for computing and displaying the absolute magnitude and direction of peak velocities for tissue using variance estimates.
U.S. Pat. No. 5,628,321 (Scheib, et al., issued May 13, 1997) describes a technique for computing many peak velocities over a cardiac cycle from the power spectrum of received pulses using a threshold to determine an optimum cardiac cycle.
U.S. Pat. No. 5,846,202 (Ramamurthy, et al, issued Dec. 8, 1998) describes color coding of blood flow velocities and using the highest mean velocity for display (Col 9, lines 7-14).
Techniques described in the foregoing patents fail to provide a color coded display of moving structure from which a user may readily observe peak structural movement parameter values.
A need exists for a robust approach to easily visualize a color-coded display of moving tissue structure such that a user may readily observe structural movement parameter values that are larger than mean values.
An embodiment of the present invention provides an ultrasound system for generating an image representative of moving cardiac structure by displaying color characteristics representative of peak values of mean parameter signals that are representative of the moving structure.
An apparatus is provided in an ultrasound machine for generating a display responsive to moving structure of a subject within a region of interest (ROI) by displaying at least one color characteristic related to a movement parameter of the structure. In such an environment the apparatus for displaying the color characteristic preferably comprises a front-end arranged to transmit ultrasound waves into the structure and then to generate received signals in response to ultrasound waves backscattered from the structure in the ROI over a time period. A processor is responsive to the received signals to generate a set of parameter signals representing values of the movement parameter within the structure during the time period and is responsive to the set of parameter signals to generate a color characteristic signal representative of a selected value larger than the mean value of the set of parameter signals. A display is arranged to display a color representation of the moving structure in response to the color characteristic signal.
A method is also provided in an ultrasound machine for generating a display responsive to moving structure within a region of interest (ROI) of a subject by displaying at least one color characteristic related to a movement parameter of the structure. In such an environment, the method preferably comprises transmitting ultrasound waves into the structure and receiving signals in response to ultrasound waves backscattered from the structure in the region of interest over a time period. A set of parameter signals representing values of the movement parameter within the structure during the time period is generated in response to the received signals. A color characteristic signal representative of a selected value larger than the mean value of the set of parameter signals is generated in response to the set of parameter signals. A color representation of the moving structure is displayed in response to the color characteristic signal.
Certain embodiments of the present invention afford an approach to visualize the color display of movement parameter values of moving structure greater than mean values in real-time with a degree of convenience and accuracy previously unattainable in the prior art.